[css21] Missing "tr{vertical-align:inherit}" in Appendix D? (default style sheet for HTML)

HTML table cells are middle aligned. (That's stupid, but...)
Therefore Appendix D contains the following rules:

thead, tbody, tfoot { vertical-align: middle }
td, th              { vertical-align: inherit }

This doesn't make much sense for me without this missing rule:

tr                  { vertical-align: inherit }


WebKit and Gecko have this inside:
<http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/css/html4.css#L200>
<http://lxr.mozilla.org/mozilla1.8/source/layout/style/html.css#206>

There is a related discussion about Opera's behaviour here:
<http://my.opera.com/community/forums/topic.dml?id=207329>

j.j.